The reduction of carbon dioxide at semiconductor electrodes has been the focus of study in recent years with the goal of developing a system for the storage of solar energy as carbon based fuel. One such fuel is methanol which can be used to replace hydrocarbon fuels without major adjustments. Metal electrodes have also been studied since they offer the possibility of superior catalytic properties and can be coupled to solid state photoelectrical cells for solar energy storage. The reduction of carbon dioxide to methanol has been demonstrated on p-GaP, n- and p-GaAs, n-Si and P-InP (M. Halmann, Nature 275 (1978 ) 115, T. Inoue, et al, Nature 277 (1979 ) 637, D. Canfield, et al, J. Electrochem. Soc. 130 (1983 ) 1772 and D. Canfield, et al, J. Electrochem. Soc. 131 (1984 ) 2518. Reduction at n-GaAs is selective with nearly 100% faradaic efficiencies. Unfortunately, at pH 4.2 a potential of -1.2 V to -1.4 V vs SCE is necessary to drive the reduction with high faradaic efficiencies although the standard potential for the reduction of carbon dioxide to methanol, derived from the value for heat of formation found in Selective Values of Chemical Thermodynamic Properties, United States National Bureau of Standards, Technical Note No. 290 -2, at pH 4.2 is only -0.563 V vs. SCE. Semiconductor electrodes are also inherently susceptible to corrosion (A. J. Bard, et al, J. Electrochem. Soc. 124 (1979 ) 1706 and H. Gerischer, J. Electroanal. Chem. 82 (1977 ) 133 ). Indeed, some of the materials that have been shown to make methanol suffer from corrosion in parallel with the electrocatalytic reduction of carbon dioxide.
Previous electrolytic reduction of carbon dioxide at metal electrodes has led to reduction of the carbon dioxide to formic acid or carbon monoxide when the electrodes were Pd, Pt and Hg. (W. Paik, et al, Electrochimica Acta 19 (1969 ) 1217, V. Kaiser, et al, Br. dB. Gesellschaft 77 (1973 ) 818, T. N. Andersen, et al, Stud. Trop. Oceanogr. 5 (1965 ) 229, P. G. Russel, et al, J. Electrochem. Soc. 124 (1977 ) 1329 and S. Kapusta, et al, J. Electrochem. Soc. 130 (1983 ) 607 ).
The present invention is directed to overcoming one or more of the problems as set forth above.